mk1-forum.net

Oneball wrote: ↑Sat Dec 09, 2023 6:08 pm

BAD942B wrote: ↑Sat Dec 09, 2023 11:37 am

You don't use a DTI like that, fit 360 protractor to crank with pointer bolted to block, turn engine over past TDC to get an idea of where the dial tops out, turn back & bring slowly up to TDC, make a note of point reading on the protractor at say 0.025" BTDC then slowly turn on to 0.025" ATDC, & note the point reading, divide by 2 & you have TDC

And seeing as how you use a stop the same way is it less accurate?

My initial thinking was because it’s at an angle, (on an a series) it will be. But does the before and after bit remove that inaccuracy?

I have found without question a stop is way more accurate than the Dial Gauge method, it's also way faster. I have both one that screws in to the cylinder head and also another for use when the head is off.

There's running clearances between many of the parts, the mains, big ends etc, using a stop you take up all those clearances and remove the ambiguity from it.

The method above when using a Dial Gauge is how it's done but it's important to take both measurements on a rising piston, ie you wouldn't say take the first reading on a rising piston, then go over TDC and take the 2nd on a falling piston. It's also best done if using a Dial Gauge, with the head removed and the Stylus over the gudgeon pin.

BAD942B wrote: ↑Sat Dec 09, 2023 11:37 am

timmy201 wrote: ↑Fri Dec 08, 2023 11:06 pm The problem with using a dial indicator to check the TDC point is that the piston will dwell at TDC for a few crankshaft degrees and you may not get a true reading. The standard method is to check it on the way up (say 1/16” before), note the mark on the crank marker, then check it on the way down at the same point (1/16”). Average the two readings to get true TDC

The same process is used for valve timing as it’s difficult to get a decent reading at full lift

When you are trying to measure TDC when the head is on, the piston stop is one of the best ways when you can’t get an accurate dial indicator reading.

You don't use a DTI like that, fit 360 protractor to crank with pointer bolted to block, turn engine over past TDC to get an idea of where the dial tops out, turn back & bring slowly up to TDC, make a note of point reading on the protractor at say 0.025" BTDC then slowly turn on to 0.025" ATDC, & note the point reading, divide by 2 & you have TDC

I thought I said exactly the same thing, except I said “crank marker” and not “protractor”?

Exactly the same method is used for a dial gauge and piston stop for the best result

Both ways are much better than just trying to measure highest point of the piston with a dial gauge